The disclosure of Japanese Patent Application No. HEI 11-37860 filed on Feb. 16, 1999 including the specification, drawings and abstract reference in its entirety.
1. Field of the Invention
The present invention relates to a vehicle vibration restraining apparatus for restraining vibrations of a vehicle by controlling at least one of a power source of the vehicle and a continuously variable transmission provided between the power source and a vehicle-driving portion and, more particularly, to an apparatus that performs a control to restrain front-rear vibrations (bucking or transient surge vibrations) of a vehicle and a control method for restraining vehicle front-rear vibrations.
2. Description of the Related Art
It is known that if a continuously variable transmission installed in a vehicle is operated to a lower speed side upon an output increase request or an acceleration request, for example a depression of an accelerator pedal or the like, the vehicle body experiences front-rear vibration at the time of completion of the speed-reducing shift. Such vibration, generally termed bucking or transient surge vibration, is caused by an inertia torque, an oscillating elasticity of a power transmission system, and the like. More specifically, when the continuously variable transmission is operated to a lower speed side upon an acceleration request or an output increase request to the power source such as an engine or the like, the rotation speed of a rotating body involved in the power transmission changes, thereby producing an inertia torque in accordance with the amount of change in the rotation speed of the rotating body (angular acceleration) and the inertia moment. The inertia torque is released when the rotation speed of the rotating body stabilizes at a target speed, approximately at the end of the speed shift. As a result, the released inertia torque temporarily increases the driving torque, so that front-rear vibration occurs despite the oscillating elasticity of the power transmission system.
Japanese Patent Application Laid-Open No. HEI 8-177997 describes an apparatus for restraining the above-described front-rear vibration of a vehicle. This apparatus restrains vehicle front-rear vibration s by controlling the transmission speed change ratio. Specifically, the apparatus determines an end timing of a speed shift based on a target speed ratio and a present speed ratio. Furthermore, the apparatus estimates a half period of vehicle front-rear vibrations expected to occur at the end of the speed shift, on the basis of the input torque to the transmission and the actual speed ratio. At a time preceding the end point of the speed shift by the half period of the vehicle front-rear vibrations, the apparatus forcibly corrects the speed change ratio to the higher speed side. Due to this apparatus design, about half the inertia torque is released during the duration between the time point preceding the shift end point by the half period of the vibrations and the shift end point. After the shift end point, the remaining inertia torque is released in the form of vibrations whose phase is opposite to that of the vehicle front-rear vibrations, so that the inertia torque offsets vehicle front-rear vibrations. In this manner, the vehicle front-rear vibrations are restrained. This control will be hereinafter referred to as xe2x80x9ctransient surge vibration restraining controlxe2x80x9d.
The apparatus described in Japanese Patent Application Laid-Open No. HEI 8-177997 performs the transient surge vibration restraining control at the time of a speed shift, although a slight oscillation remains in the power transmission system at that time. Therefore, vehicle front-rear vibrations may not be precisely restrained. To overcome this problem, an apparatus that effectively restrains vehicle front-rear vibrations by controlling both the output torque of a power source and the speed change ratio of a continuously variable transmission is proposed in, for example, Japanese Patent Application Laid-Open No. HEI 11-5460. This apparatus controls the output torque of the power source so that the drive wheel torque remains unchanged during the duration between the start of a speed shift of the continuously variable transmission and a time point preceding the end of the speed shift by half the period of the vehicle front-rear vibrations, and so the output torque reaches a target output torque at the aforementioned time point and remains at the target value thereafter, and controls the output speed of the continuously variable transmission so that the drive wheel torque remains at half a target torque from the time point preceding the end of the speed shift by half the vibration period until the end of the speed shift. The apparatus precludes oscillation of the power transmission system by optimally controlling both the output torque of the power source and the output speed of the continuously variable transmission as described above, so that vehicle front-rear vibrations can be effectively controlled.
However, the aforementioned conventional apparatuses use a specific value calculated from the speed change ratio of the continuously variable transmission and a preset total weight of a vehicle carrying an average load (i.e., the sum of the vehicle weight, an expected occupant weight, and an expected luggage weight), as a value of half the specific vibration period of the vehicle (vehicle front-rear vibration period) needed for the vibration restraining control. At specific times based on the calculated specific value, control signals and the like are outputted to the power source and the continuously variable transmission. Therefore, when the number of occupants or the vehicle-carried load changes, the control timing becomes imprecise, so that proper vibration control becomes impossible.
Accordingly, it is an object of the invention to provide a vibration restraining apparatus and a vibration restraining method capable of performing proper vibration control by sufficiently precluding vehicle front-rear vibrations even if the number of occupants or the vehicle-carried load changes.
To achieve the aforementioned and other objects, the invention provides a vehicle vibration restraining apparatus for restraining a front-rear vibration of a vehicle including a power source that produces a drive force of the vehicle, a continuously variable transmission that transmits the drive force to a vehicle-driving portion and that continuously varies a speed change ratio, a vibration restrainer that controls at least one of the power source and the continuously variable transmission so as to restrain the front-rear vibration of the vehicle, a vibration period calculator that calculates a specific vibration period of the vehicle in accordance with a state of load on the vehicle, and a timing determiner that determines a timing of a control output to the at least one of the power source and the continuously variable transmission based on the specific vibration period calculated by the vibration period calculator.
This vehicle vibration restraining apparatus calculates a specific vibration period of the vehicle in accordance with a state of load on the vehicle, and calculates a timing of a control output to the power source or the continuously variable transmission based on the calculated specific vibration period. Therefore, if the number of occupants in the vehicle or the load carried by the vehicle changes, the control output is produced at a proper time in accordance with such a change. Hence, even if the vehicle-carried load changes, the apparatus is able to properly restrain vehicle vibrations by sufficiently precluding vehicle front-rear vibrations.
In the vehicle vibration restraining apparatus, the vibration period calculator may calculate the specific vibration period of the vehicle based on either a duration between peaks of change in an output rotation speed of the power source, a duration between peaks of change in a speed of the vehicle, or a duration between peaks of change in an acceleration of the vehicle.
During front-rear vibrations of the vehicle, the vibrations appear as periodical fluctuations of the vehicle speed or acceleration. Furthermore, vehicle front-rear vibrations propagate from the vehicle-driving portion to the power source via the continuously variable transmission, so that the vibrations can also be detected as periodical fluctuations of the output rotational speed of the power source. Therefore, the vehicle vibration restraining apparatus is able to determine a duration between peaks of change in at least one of the output rotational speed of the power source, the vehicle speed, and the vehicle acceleration (i.e., a duration between a relative maximum and a relative minimum, or between a relative maximum and another relative maximum, or between a relative minimum and another relative minimum) and to determine an accurate specific vibration period of the vehicle based on the inter-peak duration.
Furthermore, in the vehicle vibration restraining apparatus of the invention, the vibration period calculator may calculate the specific vibration period of the vehicle by subjecting either an output rotation speed of the power source, a speed of the vehicle, or an acceleration of the vehicle to a fast Fourier transform.
That is, utilizing the fact that vehicle front-rear vibrations appear as periodical fluctuations of the vehicle speed, the vehicle acceleration or the output rotational speed of the power source, the vibration period calculator can subject data regarding such fluctuations to a fast Fourier transform to determine an accurate specific vibration period of the vehicle.
Further, in the vehicle vibration restraining apparatus, the vibration period calculator may calculate the specific vibration period of the vehicle based on both the drive force from the power source and an acceleration of the vehicle.
The specific vibration period of a vehicle has a correspondence to the total weight of the vehicle including the amount of load carried by the vehicle. The total weight of the loaded vehicle can be determined on the basis of a relationship between the drive force from the power source and the acceleration of the vehicle. Therefore, based on the total weight of the loaded vehicle calculated on the basis of the drive force from the power source and the vehicle acceleration, a specific vibration period of the vehicle can be accurately determined.
Still further, in the vehicle vibration restraining apparatus, the vibration period calculator may calculate the specific vibration period of the vehicle based on a value detected by a vehicle-carried load detector provided in the vehicle.
The specific vibration period of a vehicle has a correspondence to the total weight of the vehicle including the amount of load carried by the vehicle, as mentioned above. The total weight of the loaded vehicle can be determined as the sum of the mass of the vehicle, the amount of load (occupants and luggage) carried by the vehicle. Therefore, a specific vibration period of the vehicle can be accurately determined based on the detection value from the vehicle-carried load sensor.